I personally don't think they have the guys to kill off any of the Avengers.
1.Iron Man
2.Captain America
3.Thor
4.Hulk
5.Hawkeye
6.Black Widow

They all are safe. If anyone does it will be secondary characters. Personally I would be pleasantly surprised if the killed of one Of the big guns. Also I'm not a fan of the James Bond recasting. Theirs plenty of characters to make this go on for a long time without having to watch Iron Man 21 or Thor 14. Also if you kill a character off leave them gone.